This application claims priority to Korean Patent Application Number 98-29083, filed Jul. 20, 1998, and the 98-29083 application is herein incorporated by this reference in its entirety.
1. Field of the Invention
The present invention relates to a fermentation process for preparing a high yield erythritol using a salt tolerant mutant of Candida sp. [Candida magnoliae, SR101:KCCM-10160]. More specifically, the present invention relates to a process for preparing erythritol under optimal fermentation conditions for maximal erythritol production by optimizing the environmental conditions of culture, including medium component, pH, temperature, aeration rate and agitation speed.
2. Background Art
Erythritol, a four carbon sugar alcohol, is a naturally occurring substance and is widely distributed in nature. Like most of the other polyols, it is a metabolite or storage compound for seaweeds and mushrooms. Fruits like melons, grapes and pears also contain erythritol. As it is often produced by bacteria, fungi, and yeasts, erythritol also occurs frequently in fermented food systems like wines or beers, and in processed vegetables, such as soy sauce or the oriental miso bean paste.
Erythritol is a moderately sweet bulking agent with 60-70 percent of the sweetness of sucrose in a ten percent solution. Its high positive enthalpy of solution provides the crystalline material with a strong cooling effect. As it has a taste which is very close to sucrose without bitter aftertaste, it is ideal to improve the taste of a combination with intense sweeteners like aspartame.
As a small molecule, erythritol also has strong colligative properties, i.e. a strong freezing point depression and boiling point elevation effect as well as a high osmotic pressure. In combination with its low hygroscopicity and viscosity in solution, it is also very useful to reduce and control the water activity of foodstuffs.
Erythritol produced from its natural sources, such as fruits and vegetables, occurs in relatively small amounts. Consequently, these natural sources are impractical for the high yield production of erythritol. Other methods of producing erythritol include chemical manipulation and the use of micro-organisms. Chemically, erythritol is produced by reduction of meso-tartarate, oxidation and reduction of 4,6-o-ethylidene-D-glucose, hydrolysis of dealdehyde starch, or addition of hydrogen. The production of erythritol by this and other related chemical processes, however, is expensive.
Erythritol produced by microbial methods is typically grown by use of osmophilic yeasts such as with species of the genus Torulopsis, such as T. magnoliae, T. veratilis, and T candida; Endomycopsis chodati; Hansenula supelliculsa; Pichia miso; Monilliella tomentosa var. pollinis; Trigonopsis variabilis; Trichosporonoides; Candida zeylanoides; and Aureobasidium. Some bacteria such as Leuconostoc oenos can also produce erythritol. Monilliella toiiientosa var. pollinis produced erythritol on a medium containing 35.7% glucose with 45.6% yield. Erythritol production using this strain did not apply to industrial scale due to by-products such as glycerol and ribitol. Industrial production of erythritol has been performed by a mutant of Aureobasidium. The mutant was isolated and developed by cooperative study of Nikken Chemical and National Research Institute of Japan. The mutant produced erythritol with 47.6% yield on a medium containing 22.5% glucose and 2 g/L-h volumetric productivity. However, the culture with this fungus had more difficultly than that with yeast.
The present invention presents a novel process for producing a high yield erythritol by isolating a wild yeast strain of Candida sp. from nature and mutating the yeast with EMS (Ethyl-methanol sulfonate) treatment. One of the mutants has superior properties to the wild strain in erythritol yield from glucose, volumetric productivity, and salt tolerance. By using the mutant of Candida sp., the optimization of the environmental conditions of culture was performed for maximal erythritol production.